The debt ceiling drama under way right now in Washington — or, more specifically, the dramatic inability of Republicans and Democrats to reach compromise and the cheerleading of many who don't want them to — is the latest testament to an odd phenomenon in American politics. It goes by a couple of different names: increasing partisanship, political polarization, the disappearing center. And political scientists don't have a single winning theory to explain it.

"This political polarization is something that's fascinated me as a political scientist quite a bit because it's so strange," said Philipp Rehm, an assistant professor of political science at Ohio State University. "All the theories we have suggest that actually if you have a two-party system, what the parties should be doing is converging; they should be chasing the middle, the decisive swing voter. And in the U.S., the trend has been just the opposite. It's sort of a huge embarrassment for many of the theories that we have."

Income inequality in America has been growing for several decades, but so too has the gap in how risk is distributed along the income scale. In this context, risk basically means the likelihood that you think you might lose your job (as measured by the unemployment rate of a particular occupation). Historically, the workforce has included people with low-paying jobs but high job security (think unionized custodial workers), and people with decent-paying jobs but low job security (maybe high-end construction contractors).

These people, Rehm explains, make up the political center, because their interests are "cross-pressured." Higher income people are more likely to vote Republican (and lower-income people Democratic). But if you're worried you might lose your high-paying job, then you may support the party that believes in income redistribution and a strong social safety net. And if you've got great job security — even if you don't make much — then you may be less inclined to support social programs that won't benefit you.

According to Rehm's research, this "cross-pressured" group has been disappearing over the past four decades. Increasingly, most of us are now either low-income/high-risk (line-order cooks and groundskeepers), or high-income/low-risk (bank managers and lawyers): either "natural" Democrats or "natural" Republicans.

THE IDEA LOBBYMiller-McCune's Washington correspondent Emily Badger follows the ideas informing, explaining and influencing government, from the local think tank circuit to academic research that shapes D.C. policy from afar.

The underlying reasons for why this has happened have more to do with the labor market than with politics. The economy has essentially aligned risk with income, so that if you don't have much of the latter, you probably have a lot of the former, and vice versa.

He has a few hypotheses for why the economy no longer supports the type of employment that previously created large numbers of "cross-pressured" voters. There's been a dramatic decline in unionization over the past several decades. And many jobs that once offered decent salaries to workers without extensive education have now been mechanized or moved overseas.

"I don't think we can just blame the elites," Rehm said of one common explanation for political polarization. "I think there's actually something going on in the labor market that is really, really important. ... If we don't look at this, we miss a big, big story. We miss a big picture of what's going on with partisanship."

It's easy to think of examples that don't fit Rehm's model. The first that comes to mind is the group he regularly presents this research to: tenured political science professors with high income, high job security and a high likelihood of voting Democratic. Another is the population in Thomas Frank's best-selling book What's the Matter with Kansas? which attempted to understand why low-income, high-risk blue-collar Kansans (whom Rehm's theory suggests would be natural Democrats) largely vote Republican.

"The sushi-eating, Volvo-driving East Coast liberal is the exception," Rehm said. "These exceptions are pretty famous — Thomas Frank made them super famous. But Thomas Frank is on average wrong."

Based on a large-scale representative analysis of all types of occupations, all across the country, across many years, Rehm says his theory holds up in the big picture (social science, he adds, is terrible at making predictions on the individual level given the idiosyncrasies that motivate each of us once we step into a voting booth). Of course some people are single-issue voters or values voters. But Rehm has identified broad trends in the polarization of risk and the role that may play in our voting preferences — and the current recession suggests the trend will only worsen.

Among those hardest hit by the economic crisis have been people Rehm calls the "doubly unlucky" — the low-income, high-risk people. They're also among the least likely to vote and be represented in Washington.

"In the long run, according to my theory," Rehm says, "what's going to happen is the poor are going to be [even worse off], and the rich are going to be even better off. And that enlarges the gulf between the groups and will make social policy compromise even harder."

Emily Badger writes about cities and urban policy for the New York Times from the San Francisco bureau. She's particularly interested in housing, transportation, and inequality — and how they're all connected. She joined the Times in 2016 from the Washington Post.